Pressure sensor

Abstract: A pressure sensor 10 using a vibrator 11 as a pressure detection means is disclosed. The vibrator 11 includes a diaphragm valve 12. On both principal planes of the diaphragm valve 12, circular piezoelectric bodies 14a and 14b are formed respectively. On one principal plane of the piezoelectric body 14a, a first circular electrode 18a is formed. On one principal plane of the piezoelectric body 14a, a second hollow circular electrode 18b is formed outside the first electrode 18a. On one principal plane of the piezoelectric body 14b, a third circular electrode 20a is formed opposing to the first electrode 18a. On one principal plane of the piezoelectric body 14b, a fourth hollow circular electrode 20b is formed outside the third electrode 20a, opposing to the second electrode 18b. In the diaphragm valve 12, an inside circular portion 12a interposed between the first electrode 18a and the third electrode 20a and an outside circular portion 12b interposed between the second electrode 18b and the fourth electrode 20b vibrate radially in such a manner that they expand and contract in the reverse directions.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a pressure sensor and, more particularly, to the same that uses a piezoelectric-type vibrator as a pressure detection means. One such pressure sensor is, for example, disclosed in EP-A-0 221 467. Description of the Prior Art As a piezoelectric-type pressure sensor for measuring pressure by utilizing the piezoelectric effect, there was one that uses a diaphragm valve. In such a pressure sensor, the diaphragm valve is made to have a piezoelectric characteristic and a displacement of the diaphragm valve due to pressure is detected. However, in such a conventional pressure sensor, a high pressure could be detected but a minute pressure could not be detected. SUMMARY OF THE INVENTION Therefore, the principal object of the invention is to provide a pressure sensor that can detect not only a high pressure but also a minute pressure. The present invention is a pressure sensor using a vibrator as a pressure detection means, wherein the vibrator comprises: a vibrating body; a first circular piezoelectric body formed on one principal plane of the vibrating body; a second circular piezoelectric body formed on the other principal plane of the vibrating body; a first circular electrode formed on one principal plane of the first piezoelectric body and a second hollow circular electrode formed on the outside thereof; a third circular electrode formed on one principal plane of the second piezoelectric body and a fourth hollow circular electrode formed on the outside thereof. An inside circular portion interposed between the first electrode and the third electrode and an outside circular portion interposed between the second electrode and the fourth electrode vibrate radially in such a manner that they expand and contract in the reverse directions. In the piezoelectric bodies, the inside circular portion interposed between the first electrode and the third electrode, and the outside circular portion interposed between the second electrode and the fourth electrode vibrate radially in such a manner that they expand and contract in the reverse directions, thus even when the piezoelectric bodies resonate, the diameters of the piezoelectric bodies do not vary and the vibration does not leak. The vibrator is used as a pressure detection means of the pressure sensor, thereby a variation of a resonance characteristics can be detected besides the variation of pressure due to the displacement. A pressure sensor according to the invention can detect the resonance characteristic variation besides the pressure variation due to the displacement, thus a detection sensitivity to the pressure variation can be enhanced and a minute pressure can be detected as well as a high pressure. In a vibrator that is used as a pressure detection means of this pressure sensor, the diameters of the piezoelectric bodies do not vary and the vibration does not leak even when the vibrator resonates, thus the resonance characteristic and the pressure sensor characteristic can be stabilized. The detection sensitivity to the pressure variation can be enhanced, thereby a pressure sensor of a miniature size and a low cost can be obtained. The above and further objects, features, aspects and advantages of the invention will more fully be apparent from the following detailed description of embodiments, with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a front view showing one embodiment of the present invention. Fig. 2 is a plan view showing a vibrator of a pressure sensor in the embodiment of Fig. 1. Fig. 3 is a circuit diagram showing connection of a transformer and resistors to electrodes. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 is a front view showing one embodiment of the invention. A pressure sensor 10 includes a vibrator 11 shown in Fig. 2. The vibrator 11 has a diaphragm valve 12 as a vibration body. The diaphragm valve 12 is made of non-piezoelectric material such as metal or ceramics and formed by working means such as cutting, pressing and etching. On principal planes of the diaphragm valve 12, piezoelectric bodies 14a and 14b are respectively formed. The piezoelectric bodies 14a and 14b have piezoelectric properties and are formed of piezoelectric ceramics or ZnO or others. On one principal plane of the piezoelectric body 14a, a first circular electrode 18a is formed , a second hollow circular electrode 18b is formed outside the first electrode 18a. On one principal plane of the piezoelectric body 14b, a third circular electrode 20a is formed, a fourth hollow circular electrode 20b is formed outside the third electrode 20a. In addition, the diaphragm valve 12 includes an inside circular portion 12a interposed between the first electrode 18a and the third electrode 20a and an outside circular portion 12b interposed between the second electrode 18b and the fourth electrode 20b. The first electrode 18a, the second electrode 18b, the third electrode 20a and the fourth electrode 20b are so formed that the outer diameter of the inside circular portion 12a and the inner diameter of the outside circular portion 12b are almost equal to a half of the radius of the diaphragm valve 12. As shown in Fig. 3, the first electrode 18a is grounded via a resistor 22 and a primary coil of a transformer 24. The second electrode 18b is grounded via a resistor 26 and a secondary coil of the transformer 24, the third electrode 20a is grounded via a resistor 30 and the primary coil of the transformer 24. The fourth electrode 20b is grounded via a resistor 32 and the secondary coil of the transformer 24. The first electrode 18a and the third electrode 20a are grounded via an A.C. power supply 34. The first electrode 18a and the third electrode 20a are respectively connected to two input terminals of a differential circuit 36, and the second electrode 18b and the fourth electrode 20b are respectively connected to two input terminals of a differential circuit 38. The electrodes 18a, 18b, 20a and 20b are disposed and characteristics of the piezoelectric bodies 14a and 14b and a polarity of a voltage (drive signal) applied to the piezoelectric bodies are determined so that the inside circular portion 12a of the diaphragm valve 12 and the outside circular portion 12b of the diaphragm valve 12 will vibrate longitudinally in such a manner that they expand and contract in the reverse directions. According to this embodiment, the diaphragm valve 12 has a resonance characteristic determined by a shape of the diaphragm valve 12 such as a radius of it and radially vibrate in such a manner that the inside circular portion 12a and the outside circular portion 12b expand and contract in the reverse directions by conforming a frequency of the drive signal to the resonance frequency. To conform a frequency of the drive signal to the resonance frequency may be performed by self-excited vibration. When pressure is applied to the diaphragm valve 12, the diaphragm valve 12 bends. A difference of output voltages of the first electrode 18a and the third electrode 20a is measured by the differential circuit 36, and a difference of output voltages of the second electrode 18b and the fourth electrode 20b is measured by the differential circuit 38, thereby a variation of pressure and a variation of the resonance characteristic due to the bend of the diaphragm valve 12 can be detected. According to this embodiment, the variation of the resonance characteristic can be detected besides the variation of the pressure due to the displacement which was conventionally obtained. Therefore, a detection sensitivity to a pressure variation can be enhanced in accordance with Q factor of the diaphragm valve 12, thus a minute pressure can be detected besides a high pressure. In the vibrator 11, the inside circular portion 12a and the outside circular portion 12b vibrate longitudinally in such a manner that they expand and contract in the reverse directions, thus even when the diaphragm valve 12 resonates (vibrates), a diameter of the diaphragm valve 12 does not vary, and the vibration does not leak, therefore the resonance characteristic of the vibrator 11 is stabilized. The characteristics of the pressure sensor can be stabilized. Thereby the detection sensitivity to a pressure variation can be enhanced and the diaphragm valve 12 can be miniaturized and the pressure sensor 10 of a miniature size and of a low cost can be obtained. In the above embodiment, the diaphragm valve 12 is made of non-piezoelectric material, and the piezoelectric bodies having piezoelectric properties are formed on both the principal planes of the diaphragm valve 12, however the diaphragm valve 12 itself may be made of material having the piezoelectric property. It will be apparent from the foregoing that, while the present invention has been described in detail and illustrated, these are only particular illustrations and examples, and the invention is not limited to these. The scope of the invention is limited only by the appended claims.

Claims: A pressure sensor (10) using a vibrator (11) as a pressure detection means, wherein said vibrator comprises: a vibrating body (12); a first circular piezoelectric body (14a) formed on one principal plane of said vibrating body (12); a second circular piezoelectric body (14b) formed on the other principal plane of said vibrating body (12); a first circular electrode (18a) formed on one principal plane of said first piezoelectric body (14a) and a second hollow circular electrode (18b) formed on the outside thereof; a third circular electrode (20a) formed on one principal plane of said second piezoelectric body (14b) and a fourth hollow circular electrode (20b) formed on the outside thereof, an inside circular portion (12a) interposed between said first electrode (18a) and said third electrode (20a) and an outside circular portion (12b) interposed between said second electrode (18b) and said fourth electrode (20b) which vibrate radially in such a manner that they expand and contract in the reverse directions. A pressure sensor according to claim 1, wherein said vibrating body is a diaphragm valve (12b). A pressure sensor according to claim 2, wherein said diaphragm valve (12b) is made of non-piezoelectric material such as metal or ceramics and formed by working means such as cutting, pressing and etching. A pressure sensor according to claim 3, wherein said first piezoelectric body (14a) and said second piezoelectric body (14b) are made of piezoelectric ceramics. A pressure sensor according to claim 3, wherein said first piezoelectric body (14a) and said second piezoelectric body (14b) are made of ZnO.

Inventors: NAKAMURA TAKESHI, NAKAMURA, TAKESHI, NAKAMURA, TAKESHI, C/O MURATA MANUFAC. CO., LTD.
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 1994
Main classification: G01L9
IPC codes: G01L9